Understanding acral lentiginous melanoma: from the clinic to guidelines

Invasive acral Lentiginous Melanoma (ALM) is a distinct subtype of melanoma, primarily affecting non-sun-exposed extremities such as the palms, soles, and nail beds. First described by Reed in 1976. ALM is characterised by lentiginous proliferation of atypical melanocytes along the basal layer of glabrous skin. While "acral melanoma" refers broadly to melanomas arising on acral sites, "acral lentiginous melanoma" specifically denotes this lentiginous subtype. ALM is disproportionately represented among individuals with richly pigmented skin, including Black, Hispanic and Asian populations, in whom it accounts for a higher proportion of melanoma cases than in White populations. Although it represents only 2-3% of all melanomas, ALM carries a poorer prognosis, with five-year melanoma-specific survival rates averaging 80.6%. The pathogenesis of ALM remains incompletely understood. It is not primarily UV-induced but often associated with mechanical stress on weight-bearing or high-friction areas. Recurrent mutations in KIT, NF1, TERT and TP53 are frequently observed, particularly in older and Asian patients, underscoring its distinct molecular profile. Diagnosis is often delayed due to its subtle presentation as irregularly pigmented macules or patches. Histologically, ALM demonstrates lentiginous basal proliferation with dermal invasion. Management typically involves wide local excision, though advanced disease may require lymph node surgery, radiotherapy or systemic therapy. Prognosis is influenced by tumour thickness, ulceration, and sentinel lymph node involvement. Persistent disparities in outcomes highlight the need for improved awareness, earlier diagnosis, and targeted management strategies to address the biological and sociodemographic complexities of ALM.